Abstract
The self-association of proteins into symmetric complexes is ubiquitous in all kingdoms of life(1-6). Symmetric complexes possess unique geometric and functional properties, but their internal symmetry can pose a risk. In sickle-cell disease, the symmetry of haemoglobin exacerbates the effect of a mutation, triggering assembly into harmful fibrils(7). Here we examine the universality of this mechanism and its relation to protein structure geometry. We introduced point mutations solely designed to increase surface hydrophobicity among 12 distinct symmetric complexes from Escherichia coli. Notably, all responded by forming supramolecular assemblies in vitro, as well as in vivo upon heterologous expression in Saccharomyces cerevisiae. Remarkably, in four cases, micrometre-long fibrils formed in vivo in response to a single point mutation. Biophysical measurements and electron microscopy revealed that mutants self-assembled in their folded states and so were not amyloid-like. Structural examination of 73 mutants identified supramolecular assembly hot spots predictable by geometry. A subsequent structural analysis of 7,471 symmetric complexes showed that geometric hot spots were buffered chemically by hydrophilic residues, suggesting a mechanism preventing mis-assembly of these regions. Thus, point mutations can frequently trigger folded proteins to self-assemble into higher-order structures. This potential is counterbalanced by negative selection and can be exploited to design nanomaterials in living cells.
| Original language | English |
|---|---|
| Pages (from-to) | 244-247 |
| Number of pages | 17 |
| Journal | Nature |
| Volume | 548 |
| Issue number | 7666 |
| DOIs | |
| Publication status | Published - 10 Aug 2017 |
Funding
We thank S. Wolf and E. Shimoni for help with electron microscopy experiments, and J. Georgeson for setting up the microscope time-lapse. We thank members of the laboratory, D. Fass and A. Horovitz for discussions throughout the realization of this work, H. Weissman for discussions about electron microscopy, and D. Fass for invaluable feedback on the manuscript. This work was supported by the Israel Science Foundation and the I-CORE Program of the Planning and Budgeting Committee (grants 1775/12 and 2179/14), by the Marie Curie Career Integration Grants Program (number 711715), by the Human Frontier Science Program Career Development Award (number CDA00077/2015), and by a research grant from A.-M. Boucher. H.G.S. received support from the Koshland Foundation and a McDonald-Leapman Grant. Electron microscopy studies were supported by the Irving and Cherna Moskowitz Center for Nano and Bio-Nano Imaging. E.D.L. is incumbent of the Recanati Career Development Chair of Cancer Research.